Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Wet vapour

Dry saturated vapour

Superheated vapour

2. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Reversed Rankine

Rankine

Carnot

3. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

4. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

5. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

30 bar

15 bar

2 bar

6. The boiling point of ammonia is

-77.7°C

-33.3°C

-10.5°C

-30°C

7. The capillary tube, as an expansion device, is used in

Room air conditioners

All of these

Water coolers

Domestic refrigerators

8. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Receiver and evaporator

Condenser and receiver

Evaporator and compressor

9. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Much below critical temperature

At critical Temperature

Above critical temperature

10. The freezing point of sulphur dioxide is

-77.7°C

-56.6°C

-135.8°C

-75.2°C

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11. Rating of a domestic refrigerator is of the order of

0.1 ton

40 tons

10 tons

5 tons

12. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Evaporator tubes

Condenser tubes

Refrigerant cooling tubes

13. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Dew point temperature of air

Wet bulb temperature of air

Dry bulb temperature of air

14. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

None of these

Water is used as a refrigerant and lithium bromide as an absorbent

15. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Less

Unpredictable

Equally

16. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.6

0.376

0.67

17. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

T₂/ (T₂ - T₁)

18. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Takes place at constant entropy

Takes place at constant pressure

Involves no change in volume

19. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

1.25

5.12

20. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

Normal cooling

None of these

Super-cooling

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21. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

22. Which of the following statement is correct?

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

23. Which of the following is not a desirable property of a refrigerant?

Large latent heat

Low boiling point

Good electrical conductor

High risibility with oil

24. Freon group of refrigerants are

Toxic

Nontoxic and non-inflammable

Non-inflammable and toxic

Inflammable

25. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

26. The domestic refrigerator uses following type of compressor

Axial

Miniature sealed unit

Piston type reciprocating

Centrifugal

27. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Condenser

Condenser, absorber and separator (rectifier)

Absorber

28. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

Negative

None of these

Zero

29. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

Less

More for small capacity and less for high capacity

30. Most thermostatic expansion valves are set for a superheat of

20°C

15°C

10°C

5°C

Page 4 of 4

31. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

Collect vapours

32. The curved lines on a psychrometric chart indicates

Dew point temperature

Dry bulb temperature

Relative humidity

Wet bulb temperature

33. Critical temperature is the temperature above which

Water will evaporate

A gas will immediately liquefy

Water will never evaporate

A gas will never liquefy

34. For obtaining high COP, the pressure range of compressor should be

Low

High

Any value

Optimum

35. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

3.33

2.33

1.33

36. The value of C.O.P in vapour compression cycle is usually

Always more than unity

Always less than unity

Equal to unity

Any one of the above

37. Which of the following cycles uses air as the refrigerant?

Ericson

Carnot

Stirling

Bell Coleman

38. A bootstrap air cooling system has

Four heat exchangers

Three heat exchangers

Two heat exchangers

One heat exchanger

39. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Freon

Ammonia

Brine

40. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

1: 3

9: 1

1: 1

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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